bout a year ago, I picked up a G4 upgrade proc from OWC. I actually got the Mercury Extreme 1.3GHz that they offered at that time. From my experience, its been a super reliable proc. Fo rthe price I paid to go from 466MHz to over a gig, its been worth it's weight in gold. If you need the extra speed boost, totally check out the OWC branded procs. They're just as nice as the much more expensive ones.
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Electricity tastes good. No, seriously.